Sixteen years after the U.S. invasion toppled dictator Saddam Hussein, triggering a war between Islamic State militants and the U.S.-backed Iraqi government, Iraq has finally achieved some measure of stability.

But the Iraqi government isnt taking any chances that this terrorist organization, commonly known as IS or "ISIS," could regroup.

Over 19,000 Iraqis suspected of collaborating with IS have been detained in Iraq since the beginning of 2013, according to Human Rights Watch. Most of them are Sunni Muslims, according to reporting by Ben Taub of the New Yorker. Sunnis are members of the sect of Islam from which IS predominantly recruits.

Suspected terrorists are often tortured into offering confessions that justify death sentences at trial. According to Amnesty International, common forms of torture include beatings on the head and body with metal rods and cables, suspension in stress positions by the arms or legs, electric shocks, and threats of rape of female relatives.

The governments crackdown on Sunnis even those with no evidence of ties with Islamic militants sends a troubling signal about Iraqs prospects for peace.

Our research into conflict zones shows that when post-war governments use violence against citizens, it greatly increases the risk of renewed civil war.

The period after an armed conflict is fragile.

Citizens traumatized by violence wish fervently for peace. Defeated armed factions may have their sights set on revenge.

The post-war governments priority, meanwhile, is to consolidate its control over the country. Sometimes, leaders use violent repression to ensure their grip on power.

It is a risky strategy.

We studied 63 countries where civil war occurred between 1976 and 2005, including El Salvador, Sierra Leone and Sudan. The results, which were published in the academic journal Conflict, Security and Development in January, show a 95 percent increase of another civil war in places where governments engaged in the kind of torture, political imprisonment, killings and disappearances that Iraqs government is now undertaking.

Civil war is most likely to break out in former conflict zones if civilians believe they will be targeted by the state regardless of whether or not they actually support an insurgency.

Often, our results show, people respond to indiscriminate clampdowns by arming themselves. That is easy to do in conflict zones, which are home to many former rebels with extensive battlefield training and access to weapons, including both active militant groups and the remnants of vanquished insurgencies.

During former Iraqi President Husseins rule, Sunni Muslims controlled the country, and his government actively repressed Shia citizens. Since Husseins ouster, however, Iraqs government has been run by Shia Muslims.

At the time, our study of renewed fighting in conflict zones had just begun. The preliminary findings made us concerned that al-Malikis use of violence to assert control over Iraq could restart the civil war by pushing angry Sunnis into the arms of militant groups.

Unfortunately, we were right.

Starting in 2014, the Islamic State began moving swiftly from Syria where it was based to conquer major cities across neighboring western Iraq.

Iraqi Sunnis, who were excluded from politics after Husseins overthrow and fearful of government repression, did little to stop the incursion. Islamic militants increased their recruitment among Iraqi Sunnis by promising a return to Sunni dominance in Iraq.

Many Sunnis took up arms against their own government not because they supported ISs goal of establishing an Islamic caliphate across the Middle East but because they hated al-Malikis administration.

By June 2014, the Islamic State had captured Mosul, Iraqs second-largest city, just 250 miles north of Baghdad. It took three years of fighting and the combined force of Iraqi, U.S. and Kurdish troops, as well as Iranian-backed militias, to rid the country of this terrorist organization.

In September 2017, Prime Minister Adel Abdul-Abadi claimed victory over IS in Iraq. The international community turned its focus toward Syria, where Islamic militants were continuing their war on citizens and the government.

Still, the Islamic State remains a persistent and legitimate threat to both Syria and Iraq, with some 30,000 active fighters in the region. Its commanders have reportedly buried large stockpiles of munitions in Iraq in preparation for renewed war.

The Iraqi governments crackdown on Sunnis is, in part, an effort to eliminate this threat, since IS could draw renewed support from disaffected Sunni Iraqis across the border.

But many observers think Prime Minister Abdul-Mahdi is also exacting revenge on Sunnis for previously joining IS in armed warfare against Iraqs government.

Rather than prevent more fighting, our research suggests, Iraqs clampdown on Sunnis may spark another civil war.

(Eric Keels is Research Associate at One Earth Future Foundation & Research Fellow at the Howard H. Baker Center for Public Policy, University of Tennessee; Angela D. Nichols is Assistant Professor, Florida Atlantic University).